Radio frequency (RF) isolators and RF circulators are exemplary passive magnetic (or ferromagnetic) devices (PMDs), which are used in many RF communication systems to passively control the flow of electrical signals in these systems. The PMDs are constructed to have magnetic fields that are rotary in nature and act to guide electrical signals to follow the magnetic fields such that RF signals flow from one port to an adjacent port in only one direction (i.e clockwise or counterclockwise). An RF isolator is a PMD that is used to pass signals from a first port to a second port with little loss and redirection reflections at the second port to a third port, which is terminated in a desired manner, instead of allowing them to be reflected back to the first port. An RF circulator is a PMD that is used to only pass signals presented at the first port to a second port and only pass signals presented at the second port to the third port.
An exemplary RF circulator application of a PMD 10 is provided in FIG. 1. The PMD 10 is coupled to a transmitter 12 via port P1, a receiver 14 via port P2, and an antenna 16 via port P3. In this example, the dashed arrow within the body of the PMD 10 indicates the forced direction of signal flow between the ports P1, P2, and P3. In particular, RF signals will flow clockwise from port P1 to port P3, from port P3 to port P2, and from port P2 to port P1 due to the magnetic fields provided by the PMD 10. The RF signals will not flow in the reverse direction (i.e. counter-clockwise) from port P1 to port P2, from port P2 to port P3, or from port P3 to port P1 due to the same magnetic fields.
When the transmitter 12 transmits an RF transmit signal (TX SIGNAL), the RF transmit signal is passed directly from port P1 to port P3, which is coupled to the antenna 16, through the PMD 10. The RF transmit signal will not pass from port P1 to port P2, which is coupled to the receiver 14, through the PMD 10. Similarly, when the antenna receives an RF receive signal (RX SIGNAL), the RF receive signal is presented to port P3 and passed directly from port P3 to port P2, which is coupled to the receiver 14, through the PMD 10. The RF receive signal will not pass from port P3 to port P1, which is coupled to the transmitter 12. Those skilled in the art will recognize that the application of FIG. 1 is merely exemplary and that signal flow may be directed in a counter-clockwise direction in the PMD 10, as well as that the PMDs 10 may be implemented in a variety of applications.